1. Field of the Invention
The present invention relates to an insulating film and a method for forming the insulating film. The present invention also relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification and the like, a “semiconductor device” generally means any device which can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
A technique by which a thin film transistor is formed using a semiconductor thin film formed over an insulating surface has attracted attention. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (display device). As a material of a semiconductor thin film applicable to the transistor, for example, a silicon based semiconductor material is widely known. As another material, an oxide semiconductor has been attracting attention.
For example, a transistor whose active layer is formed using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) is disclosed (Patent Document 1).
A transistor including an oxide semiconductor has on-state characteristics (e.g., on-state current) superior to those of a transistor including amorphous silicon. To apply the transistor including an oxide semiconductor to a high-performance device, such a transistor is required to have further improved characteristics, and thus techniques of crystallization of an oxide semiconductor have been developed (Patent Document 2). In Patent Document 2, a technique in which an oxide semiconductor is crystallized by heat treatment is disclosed.
Patent Document 3 discloses a transistor in which a thin film containing zinc oxide (ZnO) formed by a reactive solid-phase epitaxial growth over a single crystal yttria-stabilized zirconia (YSZ) substrate is used as an active layer.